The present invention relates to fabrication of devices such as organic light emitting diodes (OLEDs). More particularly, the invention relates to a process for encapsulating or packaging OLEDs.
FIG. 1 shows a conventional OLED device 100. The OLED device comprises one or more organic functional layers 110 between first and second electrodes 105 and 115 formed on a thin substrate 101. For flexible devices, the substrate material typically comprises plastic or polymer, such as PET, PEN, PC, or PES. The electrodes can be patterned to form, for example, a plurality of OLED cells to create an OLED device (e.g., pixelated device, segmented display, or larger area illumination source). Bond pads 150, which are coupled to the first and second electrodes, are provided to enable electrical connections to the OLED cells. A cap 160 encapsulates the device to protect the OLED cells from the environment such as moisture and/or air.
Typically, the cap is bonded to the substrate with active OLED cells using polymeric resin based adhesives. After mounting the cap onto the substrate, the adhesive is cured. Curing is preferably done by UV instead of heat due to the low thermal stability of the active layers of the OLED device. Current UV processes are ineffective with plastic substrates since the substrates filter about 40-60% of the UV radiation, resulting in incomplete curing of the adhesives. To ensure that the adhesive is fully cured, the substrate is subjected to prolonged UV exposure. However, prolonged exposure to UV undesirably cause the substrates to become brittle and yellow.
As evidenced from the above discussion, it is desirable to provide a process which effectively encapsulates the device without affecting the quality and characteristics of the substrate of active components.
The invention relates to fabricating device which includes encapsulating the active components of the device with a cap. In one embodiment, the components comprise OLEDs. An adhesive is applied to the cap in regions which contact the substrate on which the active device is formed. Providing the adhesive on the substrate in regions contacting the cap is also useful. In accordance with the invention, the adhesive is partially cured to initiate the cross-linking process while remaining in a liquid phase. In one embodiment, the pre-cure comprises exposing the adhesive to radiation for less or equal to about 30 seconds. After partially curing the adhesive, the cap is mounted onto the substrate. The adhesive is then fully cured, thereby encapsulating the device. The partial curing of the adhesive prior to mounting the cap advantageously enables curing to seal the device without the need of strong curing conditions (high temperatures or prolonged UV exposure).